The invention provides improved lateral FET structure for bidirectional power switching, including AC application. The invention particularly provides enhanced OFF state voltage blocking capability by means of field shaping in the drift region to straighten out field lines and prevent curvature crowding and gradient concentration which reduces OFF state voltage blocking capability.
Copending application Ser. Nos. 390,719 now abandoned and 390,479, filed June 21, 1982, disclose AC power FET structure. The latter includes a notch extending downwardly from a top major surface to separate left and right source regions and left and right channel regions, and direct the drift region current path between the channels around the bottom of the notch. Gate electrode means in the notch proximate the channels controls bidirectional conduction.
In the preferred embodiment of the present invention, a field shaping region forms a junction with the drift region opposite the channel region junctions with the drift region. The field shaping region is referenced through diode junctions to main electrodes connected to respective source regions. In the OFF state, depletion from the first channel region junction and from the field shaping region junction spread toward each other through the drift region to straighten out field lines in the drift region and prevent curvature crowding of field lines at edges of the notch. Likewise, in the OFF state, and during the other half cycle of an AC source for example, depletion from the second channel region junction and from the field shaping region junction spread toward each other through the drift region to straighten out field lines in the drift region and prevent curvature crowding of field lines at edges of the notch. This provides higher OFF state voltage blocking capability.